In recent years, portable information terminals typified by smartphones have been actively developed. Users desire portable information terminals, which are a kind of electronic device, to be lightweight and compact.
Patent Document 1 discloses an example of a hands-free wearable device with which information can be visually obtained at any place, specifically, a goggle-type display device that includes a CPU and is capable of data communication. The device disclosed in Patent Document 1 is also a kind of electronic device.
Most wearable devices and portable information terminals include secondary batteries that can be repeatedly charged and discharged and have problems in that, because of their lightness and compactness, the time for operation is limited. Secondary batteries used in wearable devices and portable information terminals should be lightweight and compact and should be able to be used for a long time.
Examples of the secondary battery include a nickel-metal hydride battery and a lithium-ion secondary battery. In particular, lithium-ion secondary batteries have been actively researched and developed because capacity thereof can be increased and size thereof can be reduced.
Electrodes serving as positive electrodes or negative electrodes of lithium-ion secondary batteries are each formed using, for example, lithium metal or a carbon-based material.